With the recent popularization of personal computers, inkjet printers have been widely used in not only offices but also homes for producing printed records on paper, films or fabrics.
An inkjet recording system includes a method of jetting liquid droplets under pressure applied thereto by an piezoelectric element, a method of jetting liquid droplets by thermal evolution of bubbles in ink, a method of utilizing ultrasonic waves or a method of sucking and jetting liquid droplets by electrostatic force. As ink compositions for these inkjet recording methods, water-based ink, oil-based ink and solid (waxy) ink are usable. Now, water-based ink is the mainstream of inkjet recording ink from the viewpoints of production, handling, odor and safety.
The ink compositions for inkjet recording are required to have a variety of properties including good hues, high fastness to light, heat, air, water and chemicals, firm fixation to image-receiving materials and resistance to blurring thereon, excellent keeping quality, no toxicity, high purity and low manufacturing cost. For satisfying these requirements, various ideas have been applied to dyes and pigments as coloring agents and other additives, but further improvement is desirable.
For instance, it is difficult to achieve both hue and fastness at the levels required for inkjet recording ink by use of well-known dyes and pigments to which color index (C.I.) numbers are assigned. Hitherto, the Inventors have pursued studies of fast dyes having good hues and proceeded with the development of coloring agents well suited for inkjet recording. And it has been found that, while compounds capable of functioning as water-soluble dyes generally contain water-soluble groups as their substituents and an increase in number of these water-soluble groups enables enhancement of ink stability, the images formed with the ink stabilized in such a way have a drawback of tending to become blurred under high humidity conditions.